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Eye lens is more vulnerable to radiation

Mumbai: The professionals who are constantly exposed to radiation, especially the `interventional` cardiologists, must take utmost care to protect their eyes as the new studies have shown that lens of the human eye is more ionising radiation sensitive, than thought before.

Till now, the lens of the eye was considered to be a moderately radiation sensitive tissue in the body. But several new scientific studies show that it is among the most sensitive tissues, said Dr KS Parthasarathy, Raja Ramanna Fellow of the department of atomic rnergy and former secretary of Atomic Energy Regulatory Board.

Recently, the International Commission on Radiological Protection (ICRP) reduced the safe dose limit for the lens of the eye to 20mSv (millisievert) a year, averaged over five years, with no single year exceeding 50 mSv, Parthasarathy told PTI.

"The earlier dose limit was 150mSv a year," he said.

Interventional radiology and cardiology professionals have the greatest potential to receive large radiation doses to their eye lens, if precautions (such as wearing leaded glass goggles) are not taken. "Several studies have shown that these professionals do suffer from cataracts," he said.

Also, these professionals have little training in radiological protection, and seldom use protective accessories.

Normally, eye lens is crystal-clear. If it receives high enough radiation doses, it may become partly cloudy or totally opaque. Radiation protection agencies have prescribed dose limits to the lens to prevent lens opacity or cataract, he added.

There are three main forms of cataract; nuclear, cortical, and posterior sub-capsular (PSC). Among these, PSC is the least common and is associated with exposure to radiation.

Till recently, scientists believed that cataract was formed only after the lens received a typical radiation dose, called the threshold dose, of 2Gy for a single dose, and 5 Gy when the exposure occurred in a protracted way. Not any more.

Recent studies appear to show that formation of radiation induced cataracts at much lower doses than the current standards. ICRP now considers that the threshold dose for cataract is 0.5Gy.

The present ICRP recommendations must serve as a wake-up call for interventional cardiology and radiology professionals, Parthasarathy said.

Cataract analysis of 8,607 Chernobyl clean-up workers 12 and 14 years after exposure indicated that posterior sub-capsular or cortical cataracts appeared in 25% of the participants.

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